During lumpectomy, your surgeon’s goal is to take out all the breast cancer, plus a rim of normal tissue around it. This is to be sure all the cancer has been removed.

The tumor and surrounding tissue is rolled in a special ink so that the outer edges, or margin, are clearly visible under a microscope.

During or after surgery, a pathologist looks at the tissue that’s been removed to make sure there are no cancer cells in the margin. A clear, negative, or clean margin means there are no cancer cells at the outer edge of tissue that was removed. A positive margin means that cancer cells come right out to the edge of the removed tissue and have ink on them. In some cases, a pathologist may classify the margins as close, which means that cancer cells are close to the edge of the healthy tissue, but not right at the edge and don’t have ink on them.

There has been some question about how wide a clear margin should be. Some doctors want 2 mm or more of normal tissue between the edge of the cancer and the outer edge of the removed tissue. Other doctors believe that 1 mm of healthy tissue is fine. Still other doctors think that a clear margin can be smaller than 1 mm.

Because of the controversy, about 25% of women who have lumpectomy have a re-excision, which is when a surgeon reopens the lumpectomy site to remove a larger margin of cancer-free tissue. More surgery usually means more discomfort and stress for a woman and can possibly lead to more complications or side effects.

To establish a standard for lumpectomy margins, the American Society for Radiation Oncology (ASTRO) and the Society of Surgical Oncology (SSO) reviewed a number of studies. The groups issued new guidelines saying that clear margins, no matter how small as long as there was no ink on the cancer tumor, should be the standard for lumpectomy surgery. The guidelines also say that wider margins don’t lower the risk of recurrence any more than narrower margins.

The guidelines were based on a meta-analysis done by a panel of experts from both ASTRO and SSO. A meta-analysis is a study that combines and analyzes the results of many earlier studies. In this case, the results of more than 28,160 women in 33 studies published between 1965 and 2013 were reviewed. All the studies looked at women diagnosed with stage I or stage II breast cancer treated with lumpectomy and whole-breast radiation therapy.

The guidelines include several recommendations about margins after lumpectomy to remove early-stage breast cancer, including:

If there is ink on the invasive breast cancer tumor or DCIS that’s been removed, the risk of recurrence (the cancer coming back) in the same breast is doubled.

Clear margins offer the lowest risk of recurrence in the same breast; wider clear margins don’t reduce this risk any further.

Treatments after surgery (called adjuvant treatments by doctors), such as hormonal therapy, radiation therapy, and chemotherapy, reduce the risk of recurrence in the same breast. Still, even if a woman doesn’t get adjuvant treatments, there is no evidence that the clear margins need to be wider than no ink on the tumor.

Clear margins don’t need to be wider than no ink on the tumor no matter what the biological characteristics of the cancer are. So clear margin width is the same for a cancer that is hormone-receptor-positive and hormone-receptor-negative, for example.

The width of the clear margin shouldn’t affect which type of radiation therapy a woman receives.

Women younger than 40 who are diagnosed with early-stage breast cancer have a higher risk of recurrence in the same breast after lumpectomy and a higher risk of recurrence in the chest wall after mastectomy. There is no evidence that a wider margin reduces these risks.

The panel of experts who did the meta-analysis and wrote the guidelines hope that their recommendations will reduce the number of re-excision surgeries for women diagnosed with early-stage breast cancer who have lumpectomy.

“Based on the…panel’s extensive review of the literature, the vast majority of re-excisions are unnecessary because disease control in the breast is excellent for women with early-stage disease when radiation and hormonal therapy and/or chemotherapy are added to a woman’s treatment plan,” said Dr. Meena Moran, M.D., associate professor of therapeutic radiology at the Yale University School of Medicine and one of the leaders of the expert panel.

If you’ve been diagnosed with early-stage breast cancer, these guidelines are reassuring. You and your doctor will consider which type of surgery makes sense for you based on your unique situation. For many women, lumpectomy followed by radiation therapy is a good option and more attractive than mastectomy, both physically and emotionally. The meta-analysis the guidelines are based on offers peace of mind that you likely won’t need more surgery after lumpectomy if you have clear margins, no matter how small the clear margins are.

For more information on lumpectomy, including margins, visit the Breastcancer.org Lumpectomy pages.